How Much Fertilizer to Use in a Hydroponic System

Tomatoes grown hydroponically have specific nutritional needs.

In a hydroponic growing system, all the nutrients a plant needs are delivered through water, not soil or other growing medium. Different kinds of plants have different nutrient needs. How much and what kind of nutrients you add to your water depends on the kind of plant that you are growing. You can buy commercially available formulations or mix a solution yourself. If you apply a nutrient and water solution one to three times a day, you can use it for 10 to 14 days before you have to rinse the plant roots several times with fresh water to wash out any minerals that may have accumulated on the roots.

Commercial Formulations

Horticulturalists at the University of California-Davis say proprietary mixes are available that contain all the required nutritional elements your plants may need. Many nutrient formulas have been developed for particular plants such as tomatoes, a popular hydroponic vegetable. While no one formula of plant nutrients is best for all kinds of plants, all are capable of providing adequate nutrition. You do not have to buy commercial formulations. You can mix the nutrients yourself.

Foliage Plants Home Mix

Horticulturalists at the University of Alabama offer home gardeners a macronutrient formula for plants grown for their foliage, slow growing plants and plants growing under low light intensity. Macronutrients, the main plant nutrients needed by plants, are nitrogen, phosphorus and potassium. Add 4 1/2 level teaspoons calcium nitrate, 4 teaspoons magnesium sulfate, 2 1/2 teaspoons potassium nitrate and 2 teaspoons potassium phosphate to 10 gallons of water. You need to add micronutrients and chelated iron to the macronutrient solution. Mix a micronutrient solution consisting of 11/4 level teaspoons boric acid and 1/10 teaspoon manganese chloride to 1 quart of water. Add 1/2 cup of this solution to 10 gallons of macronutrient solution. Mix 1/2 level teaspoon chelated iron to 1 quart of water and add 1 3/5 cup of this to 10 gallons of macronutrient solution.

Vegetable Plants Home Mix

University of Alabama horticulturalists suggest a macronutrient formula for vegetables, rapidly growing plants and plants growing under intense light. Add 2 level teaspoons ammonium phosphate, 4 1/2 teaspoons calcium nitrate, 4 teaspoons magnesium sulfate and 4 teaspoons potassium nitrate to 10 gallons of water. Add the same formulas and amounts of micronutrients and chelated iron to this solution as you did to the solution for foliage and slow-growing plants and plants growing under low light.

Adjusting Nutrient Solution

Whether you buy a commercial nutrient formation or mix your own solution, you need to check the pH after you add the nutrients to the water. You can buy a pH meter at a store that sells garden and hydroponic supplies. Most plants grow best in a solution that has a pH of 5.5 to 6.5. If the pH is greater than 7, meaning the water is alkaline, add a few drops of white vinegar for each gallon and recheck the pH. If the solution is below 5.5, meaning it is too acidic, add 1/2 teaspoon baking soda for each gallon and recheck.